ORIGINAL: ErikElvis
Its worth it to build your own trainer. I went straight from the nexstar futaba 4ch to the JR X9303. Very good radio. Its overwhelming at first but once you learn the basics of it you can play with the other "junk" in it later. I went right ahead and bought a radio I knew I wouldnt outgrow anytime soon. The other option is to buy the next step up radio and upgrade as you go. Its just cheaper to buy a good radio up front if you know you are going to stay in the hobby.
I got the Nexstar ARF and got a 6 channel computer radio with it. I'm now on my second (or third if you consider the Avistar I flew for 2 days mine) plane, and finding that I still don't need more than 4 channels, and am finding the computer part still a little overwhelming, so am setting up the plane to not have to use it.
I got the OS 46AX with my plane, which was the best decision I have made in my 30 year life. It is so great I never want an engine that is not OS.